Jfe Steel Corporation

Katsuyuki Ichimiya

Kazukuni Hase

Shigeru Endo

Yusuke Terazawa

Shigeki Kitsuya

Kenji Hayashi

Masao Yuga

Naoki Matsunaga

Tatsumi Kimura

Minoru Honjo

Takashi Iwamoto

Yuki Toji

Tomoyuki Yokota

Keisuke Ando

Akio Ohmori

Kimihiro Nishimura

Nobuo Shikanai

Hideto Kimura

Koichi Nakashima

Yota Kuronuma

Masayuki Horie

Hirofumi Ohtsubo

Ryo Arao

Teruhisa Kinugawa

Yoshiko Takeuchi

Kazuya Tokunaga

A method for selecting a rail steel and a wheel steel comprising: selecting a rail steel and a wheel steel to be used as a rail and a wheel on an actual track, respectively, the rail steel and the wheel steel having a specific chemical composition, such that the rail comprises a head portion having a yield strength YSof 830 MPa or more, the wheel comprises a rim portion having a yield strength YSof 580 MPa or more, and a ratio YS/YSof the yield strength YSat the head portion of the rail to the yield strength YSat the rim portion of the wheel falls within a range of: 0.85&#x2264;YS/YS&#x2264;1.95 (1).

Method for selecting rail steel and wheel steel

Disclosed are a case hardened steel which is suitable as a material for producing mechanical structural parts having high rotating bending fatigue strength and impact fatigue strength at a relatively low cost, and a method of producing the same. The case hardening steel has a chemical composition containing, by mass %, C, Si, Mn, P, S, Cr, Mo, B, Ti, N, and O within a range satisfying a predetermined relationship, and Al in at least a predetermined amount in relation to the B, N, and Ti contents, with the balance being Fe and inevitable impurities, wherein &#x221a;I&#x2264;80 is satisfied, where I represents an area in &#x3bc;mof an oxide-based inclusion located at the center of a fish-eye on a fracture surface of the case hardening steel after being subjected to carburizing-quenching and tempering and subsequently to a rotating bending fatigue test.

Case hardening steel, method of producing the same, and method of producing gear parts

Provided is a steel material for high heat input welding having excellent welding heat affected zone low-temperature toughness at &#x2212;55&#xb0; C. in the case that the steel material is welded by high heat input welding with a heat input of more than 80 kJ/cm. The steel material may be used in low-temperature storage tanks, for example. The steel material for high heat input welding includes, in mass %, C: 0.04 to 0.09%, Si: 0.15 to 0.25%, Mn: 1.40 to 2.00%, P: 0.015% or less, S: 0.0005 to 0.0040%, Al: 0.030 to 0.080%, Ti: 0.005 to 0.025%, B: 0.0003 to 0.0020%, Ca: 0.0005 to 0.0030%, N: 0.0030 to 0.0060%, O: 0.0040% or less, Nb: 0.005% or less, and Mo: 0.005% or less, the balance being Fe and incidental impurities.

Steel material for high heat input welding

Excellent CTOD properties for multilayer welding joint is provided for a steel plate. The steel plate comprises a specific chemical composition with Ceq of 0.45% or less where Ceq (%)=[C]+[Mn]/6+([Cu]+[Ni])/15+([Cr]+[Mo]+[V])/5 . . . (1) and Pcm of 0.22% or less where Pcm (%)=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5 [B] . . . (2); an average effective grain size of 20 &#x3bc;m or less at a mid-thickness part of the steel plate; and porosities having an equivalent circular diameter of 200 &#x3bc;m or more, the number of the porosities per mmbeing 0.1/mmor less.

Steel plate and method of producing same

A rail achieves a high 0.2% proof stress after straightening treatment, the high 0.2% proof stress being effective at improving rolling contact fatigue resistance of the rail, by hot rolling a steel raw material to obtain a rail, the steel raw material having a chemical composition containing C: 0.70% to 0.85%, Si: 0.1% to 1.5%, Mn: 0.4% to 1.5%, P: 0.035% or less, S: 0.010% or less, and Cr: 0.05% to 1.50% with the balance being Fe and inevitable impurities; straightening the rail with a load of 50 tf or more; and subsequently subjecting the rail to heat treatment in which the rail is held in a temperature range of 150&#xb0; C. or more and 400&#xb0; C. or less for 0.5 hours or more and 10 hours or less.

Method for producing rail

A steel plate comprising, by mass %: C: 0.03% to 0.12%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and optionally one or two or more of Cu and the like. Ti/N, Ceq, Pcm, and ACR are in particular ranges, a base metal of the plate has an effective grain size of 20 &#x3bc;m or less at half the thickness of the plate, and the plate contains a particular number of complex inclusions at &#xbc; and &#xbd; of the thickness of the plate. The complex inclusions comprise a sulfide containing Ca and Mn and an oxide containing Al and having an equivalent circular diameter of 0.1 &#x3bc;m or more.

Thick steel plate having good multipass weld joint CTOD characteristics and method for manufacturing the same

A high toughness and high tensile strength thick steel plate has a plate thickness of 100 mm or more, wherein a reduction of area in a center of the plate thickness by tension in a plate thickness direction is 40% or more. Thus, a high tensile strength thick steel plate with excellent strength and toughness in a center of the plate thickness can be obtained with no need for a larger production line, even in the case of producing a high strength thick steel plate for which the addition amount of alloying element needs to be increased.

High toughness and high tensile strength thick steel plate and production method therefor

A steel plate has excellent strength and toughness in a mid-thickness part thereof, despite having a plate thickness of 100 mm or greater. The steel plate has a chemical composition containing specific amounts of C, Si, Mn, P, S, Cr, Ni, Al, N, B, and O, with the balance being Fe and incidental impurities, and having an equivalent carbon content Ceqof 0.65 or greater. The steel plate has a yield strength of 620 MPa or greater, a plate thickness of 100 mm or greater, and has a microstructure in which prior &#x3b3; grain size in a mid-thickness part of the steel plate has a maximum value, expressed as an equivalent circle diameter, of 150 &#x3bc;m or less, and a total area ratio of martensite and bainite in the mid-thickness part is 80% or greater.

A thick steel plate is provided by heating a continuously-cast slab, hot forging the continuously-cast slab using opposing dies having respective short sides differing such that when a short side length of a die having a shorter one of the short sides is taken to be 1, a short side length of a die having a longer one of the short sides is 1.1 to 3.0, allowing cooling to obtain a steel raw material, reheating the steel raw material, performing hot rolling of the steel raw material including at least two passes carried out, allowing cooling to obtain a thick steel plate, reheating the thick steel plate to at least the Actemperature and no higher than 1050&#xb0; C., rapidly cooling the thick steel plate to 350&#xb0; C. or lower, and tempering the thick steel plate at at least 550&#xb0; C. and no higher than 700&#xb0; C.

High toughness and high tensile strength thick steel plate with excellent material homogeneity and production method for same

A high-tensile-strength steel plate is provided with a new chemical composition design that guarantees the same properties as a 50 mm thick steel plate even in a steel plate with a thickness of 100 mm or greater, without the yield stress being affected by the plate thickness. By mass %, the chemical composition includes C: 0.02% to 0.08%, Si: 0.01% to 0.35%, Mn: 1.4% to 2.0%, P: 0.007% or less, S: 0.0035% or less, Al: 0.010% to 0.060%, Ni: 0.5% to 2.0%, Mo: 0.10% to 0.50%, Nb: 0.005% to 0.040%, Ti: 0.005% to 0.025%, B: less than 0.0003%, N: 0.002% to 0.005%, Ca: 0.0005% to 0.0050%, and O: 0.003% or less, with the components additionally satisfying a predetermined relationship.

High-tensile-strength steel plate and process for producing same

A weld joint with an excellent CTOD property is produced with a weld metal, using a steel plate as a base metal. The steel plate has a chemical composition including C: 0.03% to 0.09%, Si: 0.01% to 0.35%, Mn: 1.3% to 2.0%, P: 0.012% or less, S: 0.0035% or less, Al: 0.01% to 0.06%, Ni: less than 0.3%, Mo: less than 0.10%, Nb: 0.005% to 0.023%, Ti: 0.005% to 0.025%, B: less than 0.0003%, N: 0.002% to 0.005%, Ca: 0.0005% to 0.0050%, and O: 0.0030% or less, with the components additionally satisfying a predetermined relationship. The weld metal has a chemical composition including C: 0.040% to 0.090%, Si: 0.1% to 0.8%, Mn: 1.0% to 2.5%, Al: 0.020% or less, Ni: 0.1% to 1.0%, Mo: 0.05% to 0.50%, Ti: 0.005% to 0.050%, and B: 0.0015% or less, the balance being Fe and incidental impurities.

Weld joint

Provided are a steel plate having high tensile strength, high yield strength, and excellent low-temperature toughness and a method for manufacturing the steel plate. A steel plate contains 0.04% to 0.15% C, 0.1% to 2.0% Si, 0.8% to 2.0% Mn, 0.025% or less P, 0.020% or less S, 0.001% to 0.100% Al, 0.010% to 0.050% Nb, and 0.005% to 0.050% Ti and further contains Cu, Ni, Cr, Mo, and N on a mass basis such that 0.5%&#x2264;Cu+Ni+Cr+Mo&#x2264;3.0% and 1.8&#x2264;Ti/N&#x2264;4.5 are satisfied, the remainder being Fe and inevitable impurities. The area fraction of polygonal ferrite is less than 10%. The effective grain size at the through-thickness center is 15 &#x3bc;m or less. The standard deviation of the effective grain size is 10 &#x3bc;m or less.

Thick steel plate and production method for thick steel plate

There is provided a thick steel plate having good multipass weld joint CTOD characteristics for low to medium heat input and a method for manufacturing the thick steel plate. A steel plate containing, on a mass percent basis, C: 0.03% to 0.12%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and optionally one or two or more of Cu and the like, wherein Ti/N, Ceq, Pcm, and ACR are in particular ranges, a base material of the plate has an effective grain size of 20 &#x3bc;m or less at half the thickness of the plate, and the plate contains a particular number of complex inclusions at &#xbc; and &#xbd; of the thickness of the plate, the complex inclusions being composed of a sulfide containing Ca and Mn and an oxide containing Al and having an equivalent circular diameter of 0.1 &#x3bc;m or more. Steel having the composition described above is heated at a particular temperature, is then hot-rolled, and is cooled.

Thick steel sheet having excellent CTOD properties in multilayer welded joints, and manufacturing method for thick steel sheet

Provided are a thick steel plate with which a welded joint having good CTOD property is formed by low-to-medium heat input multipass welding and a method for producing the thick steel plate. The steel plate has a composition containing, by mass, C: 0.03% to 0.10%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and, as needed, one or more elements such as Cu. Ti/N, Ceq, Pcm, and ACR each fall within the specific range. The effective crystal grain size of the base metal at the center of the plate in the thickness direction is 20 &#x3bc;m or less. A specific amount of a composite inclusion including a sulfide containing Ca and Mn and an oxide containing Al having an equivalent circular diameter of 0.1 &#x3bc;m or more is present at the &#xbc;-thickness position and the &#xbd;-thickness position of the plate. The steel having the above-described composition is heated to a specific temperature, hot rolled, and cooled.

A thick, high-toughness high-strength steel plate has excellent strength and toughness in the central area through the plate thickness. The thick steel plate has a specific chemical composition and includes a microstructure having, throughout an entire region in the plate thickness direction, an average prior austenite grain size of not more than 50 &#x3bc;m and a martensite and/or bainite phase area fraction of not less than 80%. A continuously cast slab having the specific chemical composition is heated to 1200&#xb0; C. to 1350&#xb0; C., hot worked with a strain rate of not more than 3/s and a cumulative working reduction of not less than 15%, and thereafter hot rolled and heat treated.

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Tokyo, Japan

Katsuyuki Ichimiya